Radial type arc plasma generator



Oct. 31, 1961 1. H. McGxNN ETAL RADIAL TYPE ARC PLASMA GENERATOR Filed Jan. 29, 1959 Inventors: John M4 Prou, John H. /l//c Ginn,

Qu 7` e/PAfo/nel/ United States Patent On ice y 3,007,072 Patented Oct. 31, 1961 3,007,072 RADIAL TYPE ARC PLASMA GENERATOR John H.v McGinn, Philadelphia, and John W. Prout, King of Prussia, Pa., assignors to General Electric Company,

a corporation of New York Filed Jan. 29, 1959, Ser. No. 789,944

4 Claims. (Cl. 313-231) The present invention relates to a fluid stabilized electric arc device and more particularly to a fluid stabilized electric arc device having a radial type are plasma generator.

.In keepin-g with modern missile technology, it is quite 'desirable to develop components which will function satisfactorily when exposed to ultra high temperatures for short periods of time. Such components range from liners for uncooled rocket engines to surface structures of high speed vehicles which are subject to large heat fluxes as the result of aerodynamic heating. In these particular` applications, and in many others, temperatures may range up to thousands of degrees fahrenheit for only a few seconds to minutes time of exposure. In order to determine beforehand what material would be suitable for fabricating such high speed vehicle components, it would be desirable to test samples of prospective materials in an environment comparable to that inwhich they would be exposed in actual service. In this manner, tests can duplicate not only the high ternperatures, but also structural loading, thermal shock and attack by the gaseous environment to be encountered by the component in actual operational service. -A device which is useful for the rapid and economical evaluation ofmaterials Afor resistance to high temperatu-res is the huid stabilized electric arc. l

Briefly, a fluid stabilized arc mechanism usable in high temperature component testing comprises an electric arc which is condensed or constricted into a smaller circular cross-section than would ordinarily exist in an open'arc type device.` This construction generates a very, high temperature so that a superheated plasma working iluid may bev ejected through a suitable nozzle structure and used in any desirable manner. The mass flow through the nozzle structure and the composition of the plasma is of prime concern in testing high speed vehicle components where a homogeneous and smooth flowing jet or working fluid is required.

In general, in a coaxial jet-electrode arc structure the intimate coupling between the plasma discharge and the flow of the iluid ymedium used to constrict the arc, particularly in the neighborhood of the exhaust electrode, gives rise to instabilities which greatly disturb the temperature -and velocity field in the exhaust plasma. Interpretation of test data obtained under such circumtances is most hazardous. If the exhaust nozzle is made to approach-the diameter of the opposing cylindrical electrode, the plasma discharge ybecomes erratic and cannot be satisfactorily maintained.

'Consequently, the arc will usually blow-out within a second or twoy after commencement of operations. In most cases, another objection to a coaxial jet-electrode arc-discharge arrangement is the rapid change in orifice Ageometry through erosion and burning.

The present invention provides a new type of arc discharge for a lluid stabilized arc Ygenerator which overcomes the above diiculties associated with -the coaxial jetelectrode arcdischarge arrangement and permits high pressure operation by utilizing a side 'burning or radial arc` to generate the working plasma. An electrode rod .is slidably `adjustable with respect to a chamber wall electrode coaxial therewith, wherein the radial gap therebetweenis much lsmaller than the distance of the end of the electrode rod from a nozzle assembly coaxially spaced 2 therefrom. A pressurized liuid medium'is tangentially introduced in an arc chamber enclosing the electrodes to provide uni-form circumferential burning therein and to flow through the struck arc to generate a plasma working fluid discharged through the nozzle assembly.

An object of the present invention is the provision of a fluid stabilized electric arc device permitting high pressure operation by utilizingradial arc generating means.

Another object is to provide a radial type arc plasma generator which produces a homogeneous and smooth flowing jet applicable for high speed vehicle component test purposes.

Other objects and many of the attendant advantages of this invention will be readily appreciated as the same .become better understood by reference to the following detailed description when considered in connection with the accompanying drawing in which like' reference numerals designate like parts throughout the figures thereof and wherein:

FIGURE l is a cross-sectional View of a preferred embodiment of the invention.

Referring now to the drawing, there is illustrated a preferred embodiment 10 comprising a high pressure cylindrical lhousing 12 having a nozzle assembly 14 at one end thereof and a spring biased housing assembly I16 at the other end adjustably supporting thereon an axially slidable rod electrode 18 having an enlarged tip 119. A hollow cylindrical wall electrode 20, of such material as graphite, or the like, is suitably mounted within housing 12. The inner walls of wall electrode 20 define arc chamber 22. Rod electrode 18 is slidably mounted on housing assembly 16, within arc chamber 22 so that the two electrodes are substantially coaxial; i.e., the longitudinal axis of Wall electrode 20 and the longitudinal axis of rod electrode 18 are substantially coincident.

The high pressure cylindrical housing 12 is provided with a fluid medium inlet 24 having an axis tangential to the circumferential surface thereof and suitably coupled to a source of uid medium under pressure, not sho-wn. In this manner, the tluid medium flows tangentially into the housing 12 where a pressure build-up is experienced in the manner of a manifold device. A main inlet 26 is tangentially provided on the cylindrical surface of the wall electrode 20 near the base thereof and a smaller tangential auxiliary inlet 28 near the top portion thereof. In this manner, the fluid medium within the housing12 will flow tangentially into the arc chamber 22 formed by the cylindrical wall electrode 20.

The lower portion of the arc chamber 22 is enclosed by the sliding housing assembly 116 biased by a number of spring means 30 mounted on a plurality of rod means 32 -xed to a radial flange 34 integrally formed on the lower end of the high pressure cylindrical housing 12. A cylindrical chamber 36 is provided wit-hin the housing assembly 16 with an opening 38 coaxially mating with the lower opening of the wall electrode 20, as shown in the drawing. 'I'he opening 38 and the lower wall of electrode 20 are provided with a freely slidable coacting joint 40 to allow for the differential thermal expansion of the component parts of the preferred embodiment 10.

As further seen from the drawing, the circumferential surface of the cylindrical chamber 36 slidably con- ,tacts the interior wall of the housing `12 at 42 to completely seal the lower end thereof, while permitting thermal expansion of the coacting structural components.

An adjustable relief valve 44 is provided on the wall of the housing assembly 16 opening into the chamber 36 and, in turn, `into the arc chamber 22 to permit regulation therein of the desired chamber pressure and ow rate. The relief valve 44 is predeterminedly located below the main inlet 26 and suiiiciently distant from the discharge region of the arc chamber so that the structural arrangement provides suflicient space for imparting a moderate angular velocity to the fluid medium within the arc chamber 22, without rforcing too large a iluid flow through the are region. Briefly, the relief valve allows gas to be discharged yfrom the cylindrical chamber 36 to thereby increase the tota-l gas ow and increase the tangential velocity. Under s'ome operating conditions, the preferred embodiment may be possibly used with the valve 44 closed. For example, the valve would be closed when it is desirable to have all the gas discharge through the nozzle.

The nozzle assembly 14 is provided with a converging and diverging throat 46 of a predetermined design so that the cross-sectional area of the discharge region between the electrode `18 and the chamber wall electrode will be predeterminedly smaller than the cross-sec- -tional area of the throat to keep the arc from blowing downstream toward the nozzle assembly. The nozzle assembly is suitably attached, such as by bolt means 48, to the high pressure cylindrical housing. 1x2 and coacts with the cylindrical chamber 36 to axially support therebetween the interior cylindrical wall electrode 20 to prevent any relative radial movement except the differential thermal expansion of the respective structural components. As can be seen in the drawing, the wall electrode 2t) is maintained iixed in a coaxial relationship with the housing 12, the nozzle assembly 14, and the electrode 18 by a compression force generated by the spring biased axially slidable housing 16 so that the direction of flow of the plasma produced within arc chamber 22 through throat 46 of nozzle assembly 14 is also coaxial, or aligned with the longitudinal axes of the wall electrode 20 and the rod electrode 18.

To assist in anchoring the arc within the discharge region, a cylindrical wall step 50 is integrally provided on the interior of the wall electrode 20 between the nozzle assembly 14 and the tip 19 of the electrode. Further, the tip of the electrode 18 is provided with an integral enlarged tip 19 to predeterminedly reduce the cross-'sectional area of the discharge region between the wall electrode Ztl and the elect-rode rod to maintain the area smaller than the throat area 46 to prevent the arc from blowing downstream.

The electrode 18 is suitably mounted in an electrode holder 52 through collet means, not speciically shown, or by being threaded therein, or by any other well-.known fastening or supporting means.

The electrode holder may be coupled -to a remote controlled electrode actuating means, not shown, to axially slide the electrode, with respect to the sliding housing assembly 16, in a predetermined manner Iwithin the arc chamber 22 to maintain the discharge region in a desired location with respect to the nozzle assembly. An insulating bushing S4 is coaxially provided between the housing 16 and the electrode 18, or its electrode holder 52, to insulate electrically the relative structural components from each other.

In the operation of the preferred embodiment 10, prior to striking the arc, the interior portion of the high pressure cylindrical housing 12 is pressurized by injecting through the main inlet 24 a Huid medium under pressure. The iluid medium will, in .tu-rn, now tangentially into the arc chamber 22 through the main inlet 26 and through the much smaller auxiliary inlet 28. In the meanwhile, the relief valve 44 is predeterminedly adjusted for the desired chamber pressure and tlow rate, parameters dictated by the particular application. In this manner, a moderate angular velocity is imparted to the gas without forcing too large an axial tiow through the discharge region between the coacting electrode members.

Axially sliding the electrode 1-8 within the arc cha-mber 22 to electrically short the rod end-step 19 of the electrode with the wall electrode 2-0 will initially strike an are. If desirable the arc may be initiated by moving the electrode 18 forward so as to contact the nozzle and then withdrawing the electrode to the position shown and maintaining the arc, or by placing a small piece of fuse wire between the electrode and the wall. This wire will melt when power is applied and the are will continu'e. After the arc is initiated the arc discharge will be maintained between the electrode 18 and the wall electrode 20 provided the radial gap therebetween i's substantially smaller than the distance of the electrode tip 19 to the nozzle assembly end of the chamber. The tangential rotation of the fluid medium within the arc chamber 22, will cause the arc between rod electrode 18 and the wall electrode 20 to rotate with the uid mediurn within the discharge region substantially at right angles to the longitudinal axes of wall electrode 20 and rod electrode 18, and the direction of ow of the plasma through throat 46. In addition, iluid medium entering through the smaller auxiliary inlet 28 will provide a cooling layer to protect the nozzle assembly 14 from the hot plasma. In this manner, the maximum temperature obtainable will be that ofthe arc column itself, which would approximately equal 6,000 K. when air is utilized as the iluid medium.

As can Abe `seen `from FIGURE l, the sliding housing 16 is suitably grounded while the wall electrode 20 is electrically coupled to a suitable power source, such as the D.C. power supply shown in the drawing. The circuit is completed by coupling the electrode 18 to the power source through a resistance element. The re-- sistance is placed in the circuit so that approximately 50 percent of the available D.C. power is dissipated in the ballast resistance. This tends to stabilize the are.

It should be understood, of course, that the foregoing disclosure relates to only a preferred embodiment of the invention and that it is intended to cover all changes and modifications of the example of the invention herein chosen for the purposes of the disclosure, which do not constitute departures from the spirit and scope of the invention as set forth in the appended claims.

What is claimed is:

l. An arc plasma generator comprising a high pressure cylindrical housing, a hollow cylindrical wall electrode within said housing', a rod electrode mounted with-v in t-he cylindrical wall electrode, the longitudinal axes of said wall electrode and said rod electrode being substantially coincident, a nozzle assembly secured to said housing, inlet means for introducing a pressurized fluid medium within said wall electrode, means for connect-V ing said wall electrode and said rod electrode to a source of unidirectional electrical current, the distance between the wall electrode and the rod electrode being such that arcs between said electrodes are substantially transverse to the longitudinal axes of the rod and wall electrodes.

2. An arc plasmal generator comprising a housing assembly, a hollow substantially cylindrical wall electrode mounted within said housing assembly, a rod electrode mounted within said wall electrode and substantially coaxial therewith, means for connecting a source of electrical power to said -rod andV wall electrodes to establish an arc between them, tangential fluid inlet means in said housing assembly and said cylindrical wall electrode for introducing within the wall electrode pressurized fluid havin-g a component of angular velocity about said rod electrode, nozzle means mounted on said housing assembly in substantial coaxial relationship with the rod electrode and the wall electrode to discharge the plasma produced within the wall electrode, the spacing between said rod electrode and said wall electrode and said nozzle means being such that arcs will be established only between t-he rod electrode and the wall electrode, and will be substantially transverse to the direction of ow of plasma through the nozzle means. y

3. An arc plasma generator comprising a high pressure `cylindrical housing, a hollow cylindrical wall electrode within said housing, said wall electrode having a step in the inner wall portion thereof, a rod electrode having an enlarged tip mounted within the cylindrical wall electrode, the longitudinal axes of said wall electrode and said rod electrode being substantially coincident, a nozzle assembly mounted on said housing, i11- let means for introducing a pressurized fluid wit-hin said wall electrode, said inlet means causing said fluid to rotate around said rod electrode, means for connecting said wall electrode and said rod electrode to a source of electrical power, the distance between said wall electrode and said rod electrode being such that arcs between said electrodes are substantially transverse to the longitudinal axes of the rod and wall electrodes and strike the wall electrode at or below the step.

4. An arc plasma generator comprising a high pressure cylindrical housing, a hollow cylindrical wall electrode within said housing, a rod electrode mounted within said wall electrode so that the longitudinal axes of said wall and rod electrodes are substantially coincident, a nozzle assembly having a central opening mounted in one endo-f said cylindrical housing, means for connecting a source of electrical energy between said wall and rod electrodes, said nozzle assembly providing an outlet for the plasma produced by arcs between the rod electrode and the wall electrode, the direction of ow of the plasma through the nozzle being substantially aligned with the longitudinal axes of the rod and wall electrodes, the Wall and rod electrodes being so positioned that the electrical arcs between them are substantially at right angles to their longitudinal axes and transverse to the direction of ow of the plasma produced, through said nozzle, said arcs rotating substantially with the iluid introduced into said wall electrode.

References Cited in the tile of this patent UNITED STATES PATENTS 2,819,423 Clark Jan. 7, 1958 2,826,709 Von Ardenne Mar. 11, 19'5'8 2,850,662 Gilruth et al. Sept. 2, 1958 2,858,411 Gage Oct. 28, 1958 FOREIGN PATENTS 635,335 Great Britain Apr. 5, 1950 

